1. Field of the Invention
The present invention relates to a method of producing Indium Tin Oxide (hereinafter, referred to as ITO) powder. More specifically, the present invention relates to a method of producing ITO powder suitable for production of an ITO sintered body of high density.
2. Prior Art
An ITO powder is used for production of an ITO sintered body, and contains tin oxide in an amount of usually from 2 to 20 wt %. An ITO sintered body is used as a target for producing an ITO thin film by a sputtering method. An ITO thin film is utilized, because of its high electric conductivity and excellent transparency, as a transparent electric conductive film for a liquid crystal display.
When a target made of an ITO sintered body of high density is used, an ITO thin film having high electric conductivity can be obtained, therefore, it is known that a high density sintered body having a relative density of 99% or more is suitable as an ITO sintered body used for a target.
Since an ITO sintered body is produced by sintering an ITO powder, an ITO powder giving a high density ITO sintered body is required.
An ITO powder for production of an ITO sintered body is produced by obtaining a precipitate containing indium and tin from an aqueous solution containing indium ions and tin ions, then, filtrating this, and calcinating the resulted precipitate. In conventional methods of producing an ITO powder, an aqueous solution prepared by dissolving InCl3 and tetravalent tin salt SnCl4 in water is used as the aqueous solution containing indium ions and tin ions, an alkali aqueous solution such as ammonia water and the like is dropped on this aqueous solution to obtain a precipitate containing indium and tin, then, this is filtrated, and the resulted precipitate is calcinated to obtain an ITO powder (for example, Japanese Patent Application Laid-Open (JP-A) Nos. 7-21831 and 7-247162). However, ITO powders produced by these methods are not sufficient for production of a high density ITO sintered body.